Pemetrexed disodium is chemically described as L-Glutamic acid, N-[4-[2-(2-amino-4,7-dihydro-4-oxo-1H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl]-disodium salt heptahydrate, represented by the chemical structure of Formula (I).

Pemetrexed is an anti-folate anti-neoplastic agent that exerts its action by disrupting folate-dependent metabolic processes essential for cell replication. It is believed to work by inhibiting three enzymes that are required in purine and pyrimidine biosynthesis—thymidylate synthase (TS), dihydrofolate reductase (DHFR), and glycinamide ribonucleotide formyl transferase (GARFT). Pemetrexed is available in the market under the brand name ALIMTA®.
Taylor et al., in U.S. Pat. No. 5,344,932 describe pemetrexed, its related compounds and pharmaceutically acceptable cation.
Chelius et al., in WO 01/14379 A2 disclose pemetrexed disodium crystalline hydrate Form I and process for preparation thereof.
Chelius et al., in WO 01/62760 disclose pemetrexed disodium heptahydrate crystalline Form II and process for the preparation thereof.
Journal of Organic Process Research & Development, Volume 3, 1999, page 184 describes a process for the preparation of pemetrexed diacid.
Busolli et al., in WO2008021411 disclose process for preparation of pharmaceutically acceptable salt of pemetrexed diacid.
Busolli et al., in WO2008021405A1 disclose seven crystalline forms of pemetrexed diacid designated as Form A, B, C, D, E, F, & G and processes for preparation thereof.
There remains a continuing need for new solid forms of pemetrexed disodium and diacid that are sufficiently stable, and the processes of preparation amenable to scale up to production quantities.